The present invention relates to a sampling tube-type smoke detector which suctions air into a sampling tube from a monitored area and optically detects smoke particles floating in the air using a laser beam, and more particularly to a sampling tube-type smoke detector which includes a smoke detection device and an aspirator aligned in a straight line and formed compactly.
Conventionally, a high sensitivity smoke detector which detects slight smoke is used in a clean room, such as a computer room, in a hospital, a semiconductor manufacturing facility and the like. The highly sensitive smoke detector in this invention suctions air from a sampling tube (synonymous with pipe) installed in a monitored area and optically detects the number of particles floating in the air using a laser beam. Thus, a highly sensitive smoke detector with a sampling tube is hereafter designated a sampling tube-type smoke detector. As shown in FIG. 11, this sampling tube-type smoke detector comprises a sampling tube 101 with suction openings 102 which suctions in air from a monitored area, a smoke detection device 103 which detects smoke particles contained in the suctioned air connected to the sampling tube 101, and an aspirator 108 which is formed in the downstream of the smoke detection device 103.
The sampling tube 101 is formed in a monitored area and comprises a detection line 101a with multiple suction openings 102 every 1–2 meters (1–2 m=about 1–2 yards apart) prescribed spacing and a connection line 101b which guides air to the smoke detection device 103 from the detection line 101a. Additionally, the smoke detection device 103 connected to the sampling tube 101 is equipped with a laser diode 104a which is a light emitting device and a photodiode 104b which is a photo detector. A chamber 107 is formed in the downstream of the smoke detection device 103 and the aspirator 108 is installed in the interior of the chamber 107. The smoke detection device 103, the chamber 107 and the aspirator 108 are dedicated to a detector main body 100 which consists of a cube-type configuration, wall surfaces and the like in formation of the chamber.
The laser diode 104a generates diffused light extended along the direction of the optical axis which is condensed with an image-formation lens located on the optical axis, and performs image-formation in the flow path of the smoke detection device 103. Smoke particles are carried to the image-formation position. The light from the laser diode 104a produces scattered light as a result of these smoke particles. This scattered light is received by the photodiode 104b located in a position which makes an optical axis of the light from the laser diode 104a at a predetermined degree angle and generates a pulse signal. A signal processing part 106 detects smoke particles generated by a fire by performing signal processing. Also, air passing through the smoke detection device 103 is discharged in the chamber 107. Subsequently, this air is discharged outside by the aspirator 108 installed in the chamber 107.
Such a sampling tube-type smoke detector, for instance, the system in the first conventional example shown in FIG. 12 is used. In this first conventional example, a smoke detection device 103 and an aspirator 108 constitute a sampling tube-type smoke detector, which are placed in a detector main body 100 resembling a cube-type shape. The smoke detection device 103 comprises a lead-in tube 103a connected with a sampling tube 101. A smoke sensor unit 104 is located in the intermediate part of the lead-in tube 103a, detects smoke particles and is arranged in a corner of the detector main body 100. Additionally, the smoke sensor unit 104 in the downstream of the lead-in tube 103a is equipped with an airflow sensor 105 for performing clogging detection in the lead-in tube 103a. The aspirator 108 has a motor-actuated, centrifugal-type fan and discharges air at a predetermined flow rate to the outside of the detector main body 100. The aspirator 108 is arranged in a corner of the smoke detection device 103 on the opposite side of the detector main body 100.
In the case of this first conventional example, segments other than the smoke detection device 103 in the detector main body 100 and the aspirator 108 are hollow and form a chamber 107. Once air suctioned through a sampling tube 101 passes the smoke detection device 103 and is discharged into the chamber 107, subsequently the aspirator 108 discharges the air to the outside of the detector main body 100. With the form of the chamber 107, the air suction state in the sampling tube 101 can be stabilized by making the pressure inside the chamber 107 low as air is suctioned. Thus, in the first conventional example, since the chamber 107 is formed of the entire detector main body 100, the signal processing part involving the smoke sensor unit 104, the power circuit of the aspirator 108, processing of the detection signal from the smoke sensor unit 104, and the like are separately located external of the detector main body 100.
As a sampling tube-type smoke detector, the system in the second conventional example shown in FIG. 13 is used. In this second conventional example, a smoke detection device 103 and an aspirator 108 which constitute the sampling tube-type smoke detector are the same as that of the above first conventional example concerning the point of view of being placed in a detector main body 100 which resembles a cube-type shape. In addition, those which have a smoke sensor unit 104 the same as that of the first conventional example are also used for detection of smoke particles. However, unlike the first conventional example, in the second conventional example, the flow path from a sampling tube 101 to the inlet port of the smoke detection device 103 connected with the aspirator 108 is formed in a single sequence. Specifically, the smoke detection device 103 is a lead-in tube 103a. The lead-in tube 103a is located in the intermediate section connected with the sampling tube 101 and comprises the smoke sensor unit 104 which detects smoke particles. The lead-in tube 103a of the smoke detection device 103 forms a direct connection to the aspirator 108. An airflow sensor 105 is formed in the downstream of the smoke sensor unit 104 similar to the first conventional example.
The aspirator 108 is driven by a motor comparable to the first conventional example, has a centrifugal-type fan, and discharges air at a predetermined discharge flow rate to the outside of the smoke detection device 103. The fan's rotational axis makes an angle of 90 degrees with the upper part of the lead-in tube 103a. Consequently, the lead-in tube 103a from the smoke sensor unit 104 bends at an angle of 90 degrees in the downstream part. Thus, without forming a chamber, the inflow of the smoke detection device 103 to the aspirator 108 forms the air duct, and the smoke detection device 103 can be formed compactly. Since in the segment which was the chamber of the detector main body 100 in the first conventional example can be made to create space in the second conventional example, a signal processing part 106 which performs management of smoke particle detection signals and the like from the smoke sensor unit 104 can also be installed in the interior of the detector main body 100.
However, these conventional sampling tube-type smoke detectors have specific limitations which are described below. The above-mentioned first conventional example suctions air by using the entire detector main body as a chamber and stabilizes the suction state of the sampling tube.
However, to acquire effective stabilization a large-sized chamber is essential. On the other hand, within the constraints of the magnitude of the sampling tube-type smoke detector, target objective stabilization is problematic. Within the chamber, there are existing cases in the interior where a portion of the flow stagnated, which does not necessarily contribute to suction stabilization. Furthermore, in the first conventional example, miniaturization is difficult as most of the main body is used as a chamber. As the signal processing from the smoke sensor unit, the power circuit and the like are located external of the detector main body, a lot of space is required for the entire device.
Besides, the above-described second conventional example, without a formed chamber the flow path guides the air from the smoke detection device directly to the aspirator and miniaturization is achieved. However, due to a limitation in the bulkiness of the detector main body, the rotational axis of the fan of the aspirator is oriented so that it becomes the lead-in tube of the smoke detection device with an angle of 90 degrees approximately. Therefore, a flow path of 90 degrees must bend. In the section where the flow path bends, pressure loss occurs in the airflow, and a comparatively large-sized fan needs to be used as the aspirator.
This invention introduces a novel approach to solve the above-mentioned limitations, which reduces the airflow pressure loss in the flow path from the smoke detection device to the aspirator, and aims at providing a sampling tube-type smoke detector which has a compact smoke detection device and can be driven by a small-sized fan.